Joining structure and method for manufacturing same

ABSTRACT

A joint structure is formed by joining a first plate-shaped member made of steel and a second plate-shaped member made of steel that is overlapped on the first plate-shaped member and that is formed in a long shape. A surface of the first plate-shaped member and both edge portions of the second plate-shaped member along a longitudinal direction are joined by a weld metal.

TECHNICAL FIELD

The present invention relates to a joint structure and a method formanufacturing the same, more specifically relates to a joint structuresuitable for, for example, a structural member for an automobile and amethod for manufacturing the same.

BACKGROUND ART

In recent years, in order to enhance collision safety while reducingweight of a vehicle body with reducing a CO₂ emission amount as anobject, a method of using a high tensile steel plate or partiallyreinforcing a necessary place with a reinforcing material is known.Patent Literatures 1 and 2 disclose a joint body manufactured by joiningtwo metal members, that is, a first metal member and a second metalmember by laser welding. Patent Literature 1 discloses that a weldingmark of the laser welding is a pair or plural pairs of straight linesparallel to each other. Patent Literature 2 discloses that a weldingmark of the laser welding has a plurality of C-shaped portions arrangedcontinuously, and parts of the adjacent C-shaped portions overlap.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2001-507993

Patent Literature 2: JP-A-2014-15206

SUMMARY OF INVENTION Technical Problem

In the joint bodies disclosed in Patent Literature 1 or 2, there isstill room for improvement in joining strength between the first metalmember and the second metal member. Therefore, the joint bodies are notsuitable for processing by, for example, hot stamping (hot press). Thatis, when these joint bodies are processed by hot stamping, due toinsufficient joining strength, particularly insufficient joiningstrength of a joint portion between the first metal member and an edgeportion of the second metal member, the first metal member and thesecond metal member may be partially or entirely peeled off from theedge portion.

Further, when an external force is applied to the hot stamping componentat the time of a collision accident, the first metal member and thesecond metal member can be peeled off, so that a sufficient reinforcingeffect cannot be obtained. Further, since laser processing equipment isexpensive, it is a factor that increases product cost.

The present invention has been made in view of the problems describedabove, and an object thereof is to provide a joint structure that hashigh joining strength and can be manufactured at low cost, and a methodfor manufacturing the same.

Solution to Problem

The present invention includes a configuration of the following (1).

-   (1) A joint structure formed by joining a first plate-shaped member    made of steel and a second plate-shaped member made of steel that is    overlapped on the first plate-shaped member and that is formed in a    long shape,

wherein a surface of the first plate-shaped member and both edgeportions of the second plate-shaped member along a longitudinaldirection are joined by a weld metal.

A preferable embodiment of the present invention includes configurationsof the following (2) to (5).

-   (2) The joint structure according to (1), wherein a bent portion is    formed on an overlapping surface between the first plate-shaped    member and the second plate-shaped member.-   (3) The joint structure according to (1) or (2), wherein the first    plate-shaped member and the second plate-shaped member are further    joined to each other in an overlapping surface between the first    plate-shaped member and the second plate-shaped member.-   (4) The joint structure according to any one of (1) to (3), wherein    at least one of the first plate-shaped member and the second    plate-shaped member is a steel material for hot stamping.-   (5) The joint structure according to any one of (1) to (4), which is    a structural member for an automobile.

The present invention includes a configuration of the following (6).

-   (6) A method for manufacturing a joint structure formed by joining a    first plate-shaped member made of steel and a second plate-shaped    member made of steel that is overlapped on the first plate-shaped    member and that is formed in a long shape, the method including:

a step of overlapping the first plate-shaped member and the secondplate-shaped member; and

a welding step of joining each of both edge portions of the secondplate-shaped member along a longitudinal direction to the firstplate-shaped member by an arc welding or a laser-arc hybrid welding.

A preferable embodiment of the present invention includes configurationsof the following (7) to (10).

-   (7) The method for manufacturing a joint structure according to (6),    wherein a bending is performed on an overlapping surface between the    first plate-shaped member and the second plate-shaped member.-   (8) The method for manufacturing a joint structure according to (6)    or (7), further comprising joining the first plate-shaped member and    the second plate-shaped member to each other in the overlapping    surface between the first plate-shaped member and the second    plate-shaped member by any welding of a laser welding, a plasma    welding, a TIG welding, or a laser-TIG hybrid welding.-   (9) The method for manufacturing a joint structure according to any    one of (6) to (8), wherein at least one of the first plate-shaped    member and the second plate-shaped member is a steel material for    hot stamping.-   (10) The method for manufacturing a joint structure according to any    one of (6) to (9), wherein the joint structure is a structural    member for an automobile.

Advantageous Effects of Invention

According to the joint structure and the method for manufacturing thesame of the present invention, the joint structure has high joiningstrength, and the joint structure can be manufactured at low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a joint structure according to anembodiment of the present invention.

FIG. 2A is a perspective view of a modification of the joint structureaccording to the embodiment of the present invention.

FIG. 2B is a cross-sectional view taken along a line A-A of FIG. 2A.

FIG. 3 is a perspective view of the joint structure bent along a lineB-B of FIG. 2A.

FIG. 4 is a cross-sectional view of another modification of the jointstructure according to the embodiment of the present invention.

FIG. 5 is a perspective view showing an example of a B pillarmanufactured by hot-stamping the joint structure according to theembodiment of the present invention.

FIG. 6 is a perspective view showing another example of a B pillarmanufactured by hot stamping the joint structure according to theembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of a joint structure according to the present invention isdescribed in detail based on the drawings.

FIG. 1 is a perspective view of a joint structure manufactured by amethod for manufacturing the joint structure according to the presentembodiment. As shown in FIG. 1, the joint structure 10 includes a firstplate-shaped member 11 made of steel and a second plate-shaped member 12made of steel as a reinforcing material, which is formed into a longshape narrower than the first plate-shaped member 11.

The second plate-shaped member 12 is overlapped on a surface 11 a of thefirst plate-shaped member 11. Both edge portions 12 a along alongitudinal direction (X direction in the drawing) of the secondplate-shaped member 12 and the surface 11 a of the first plate-shapedmember 11 are joined by a weld metal (bead) 13 formed by an arc weldingor a laser-arc hybrid welding. The weld metal (bead) 13 may be formedcontinuously along both the edge portions 12 a or may be formedintermittently. However, as described later, in the case where bendingis performed along an imaginary line B (see FIG. 2A) set on anoverlapping surface 14, the weld metal (bead) 13 is preferably formedcontinuously in order to correspond to a stress generated at the time ofbending.

A material of the first plate-shaped member 11 and the secondplate-shaped member 12, which are made of steel, is not particularlylimited as long as it is pure iron and iron alloy, and examples thereofinclude mild steel, carbon steel, and stainless steel.

The first plate-shaped member 11 and the second plate-shaped member 12can also be subjected to surface treatment for forming a coating such asan electrically low element or work piece, an insulating substance, anda passivation film in order to preventing rust, and the like. Examplesthereof include zinc plating, chromium plating, nickel plating, aluminumplating, tin plating, resin coating, and ceramic coating.

Both the edge portions 12 a of the second plate-shaped member 12 and thesurface 11 a of the first plate-shaped member 11 are joined with afiller metal (welding wire) by an arc welding or a laser-arc hybridwelding. Therefore, both the edge portions 12 a of the secondplate-shaped member 12 can be joined in a wide area, and joiningstrength is improved as compared with joining by a spot welding, a laserwelding, or the like. Further, by appropriately selecting components ofthe filler metal, it is possible to design joining strength at a jointportion. As for a material of the filler metal, a welding wire or awelding rod which is generally used is applicable as long as the weldmetal 13 is a Fe-based alloy.

In the laser-arc hybrid welding, a laser is added as a heat source in anarc welding method as a heat source and wire supply method. The methodis advantageous in that the welding speed is higher than that of anordinary arc welding method.

In the embodiment shown in FIG. 1, both the edge portions 12 a along thelongitudinal direction of the second plate-shaped member 12 are weldedto the first plate-shaped member 11 by arc welding or laser-arc hybridwelding, but edge portions 12 b extending in a direction (shortdirection) which intersect the both edge portions 12 a of the secondplate-shaped member 12 may also be welded to the first plate-shapedmember 11 by an arc welding or a laser-arc hybrid welding. In this way,by welding the second plate-shaped member 12 to the first plate-shapedmember 11 over an entire periphery of the edge portions 12 a and 12 b,water or the like penetrating into a gap between the first plate-shapedmember 11 and the second plate-shaped member 12 can be prevented, andcorrosion resistance is significantly improved.

The first plate-shaped member 11 and the second plate-shaped member 12welded by an arc welding or a laser-arc hybrid welding may be bent toform a formed article. Depending on a degree of bending or strengthrequired for the joint structure 10, in the case where only both edgeportions 12 a of the second plate-shaped member 12 are welded by an arcwelding or a laser-arc hybrid welding, the joint structure 10 may haveinsufficient joining strength or bending strength. In particular, when awidth of the second plate-shaped member 12 is wide and a distancebetween the two edge portions 12 a is large, strength may beinsufficient.

FIG. 2A is a perspective view of a joint structure 10A according to amodification in which the front surface 11 a of the first plate-shapedmember 11 and the both edge portions 12 a of the second plate-shapedmember 12 are joined by an arc welding or a laser-arc hybrid welding,and the overlapping surfaces 14 of the first plate-shaped member 11 andthe second plate-shaped member 12 are further joined by a laser welding.FIG. 2B is a cross-sectional view taken along a line A-A of FIG. 2A.

In the joint structure 10A according to the modification, as shown inFIG. 2A and FIG. 2B, the overlapping surfaces 14 of the firstplate-shaped member 11 and the second plate-shaped member 12, in whichboth the edge portions 12 a are joined to the first plate-shaped member11 by an arc welding or a laser-arc hybrid welding, are joined by alaser welding by plural pairs of joint portions 15 arranged along thelongitudinal direction (X direction in FIG. 2A) of the secondplate-shaped member 12 and formed to face to each other in a widthdirection of the second plate-shaped member 12. This further improvesthe joining strength between the first plate-shaped member 11 and thesecond plate-shaped member 12.

The joint structure 10A thus formed is bent along an imaginary line B(see FIG. 2A) set on the overlapping surface 14, and is processed into aformed article 20 shown in FIG. 3 by forming a bent portion 16.

The bent portion 16 (imaginary line B) is preferably set so as to passsubstantially the center of a pair of the joint portions 15 formed toface to each other in the width direction of the second plate-shapedmember 12. Accordingly, a force acting at the time of bending actsequally on the left and right to improve shape accuracy of the formedarticle 20.

Accompanied with bending, a shearing force acts on the joint portionbetween the first plate-shaped member 11 and the second plate-shapedmember 12. In the case where the first plate-shaped member 11 and thesecond plate-shaped member 12 are joined only by a spot welding or alaser welding, the joining strength of the edge portions 12 a of thesecond plate-shaped member 12 with the first plate-shaped member 11 maybe weak, and the second plate-shaped member 12 may be peeled off fromthe edge portions 12 a.

However, in the joint structure 10A of the embodiment, the firstplate-shaped member 11 and both the edge portions 12 a of the secondplate-shaped member 12 are joined by an arc welding or a laser-archybrid welding, and the overlapping surfaces 14 of the firstplate-shaped member 11 and the second plate-shaped member 12 are joinedin a plurality of portions by a laser welding. Therefore, the joiningstrength is high, and the first plate-shaped member 11 and the secondplate-shaped member 12 are prevented from being peeled off by bending.

In the case where the joint structures 10 and 10A are structural membersfor an automobile requiring high strength such as pillars, it ispreferable to use a steel material for hot stamping as the firstplate-shaped member 11 and the second plate-shaped member 12. In thecase where the joint structures 10 and 10A are made of the steelmaterial for hot stamping, bending is performed by hot stamping (hotworking) that is processed in a state of heating to a temperature of800° C. or higher. Accordingly, accurate forming is possible.

FIG. 4 is a cross-sectional view of a joint structure according toanother modification in which the overlapping surfaces 14 of the firstplate-shaped member 11 and the second plate-shaped member 12, in whichthe edge portions 12 a are joined by an arc welding or a laser-archybrid welding, are joined by a plasma welding, a TIG welding, or alaser-TIG hybrid welding.

In a joint structure 10B of the modification, the first plate-shapedmember 11 and both the edge portions 12 a of the second plate-shapedmember 12 are joined with the weld metal 13 formed by an arc welding ora laser-arc hybrid welding, and the overlapping surfaces 14 of the firstplate-shaped member 11 and the second plate-shaped member 12 are furtherjoined firmly in a plurality of portions by joint portions 17 formed bya plasma welding, a TIG welding, or a laser-TIG hybrid welding.

In this way, in the first plate-shaped member 11 and the secondplate-shaped member 12, both the edge portions 12 a are joined to thefirst plate-shaped member 11 by an arc welding or a laser-arc hybridwelding, and the overlapping surfaces 14 of the first plate-shapedmember 11 and the second plate-shaped member 12 are further joinedfirmly in a plurality of portions by any welding of a laser welding, aplasma welding, a TIG welding, and laser-TIG hybrid welding, so that thefirst plate-shaped member 11 and the second plate-shaped member 12 canbe formed by hot stamping and are suitably used as the structural memberfor an automobile.

In the laser-TIG hybrid welding, a laser is added as a heat source in aTIG welding method as a heat source and wire supply method. The methodis advantageous in that penetration (penetrability of two plates) isdeeper and the welding speed is higher than those of an ordinary arcwelding method.

For example, FIG. 5 shows an example of a B pillar 30 (an example of thestructural member for an automobile) manufactured by processing thejoint structures 10, 10A, and 10B with hot stamping. The B pillar 30 isformed by joining one second plate-shaped member 12 by welding to a partof the first plate-shaped member 11 required for reinforcement and thenintegrally forming them by hot stamping.

The B pillar 30 shown in FIG. 6 is formed by joining two secondplate-shaped members 12 to the first plate-shaped member 11 at positionswhich are ridge line portions of the B pillar 30, respectively, andbending the first plate-shaped member 11 and the second plate-shapedmembers 12 by hot stamping on the overlapping surface 14 between thefirst plate-shaped member 11 and the second plate-shaped member 12.

Examples of the structural member for an automobile to which the jointstructures 10, 10A, and 10B can be applied include a side sill, a floorcross member, a roof side rail, and a center tunnel cover other than theB pillar 30.

The present invention is not limited to the embodiments andmodifications described above, and modifications, improvements, or thelike can be made as appropriate.

As described above, the present description discloses the followingmatters.

-   (1) A joint structure formed by joining a first plate-shaped member    made of steel and a second plate-shaped member made of steel that is    overlapped on the first plate-shaped member and that is formed in a    long shape,

wherein a surface of the first plate-shaped member and both edgeportions of the second plate-shaped member along a longitudinaldirection are joined by a weld metal.

According to the configuration, it is possible to manufacture a jointstructure having high joining strength at low cost.

-   (2) The joint structure according to (1), wherein a bent portion is    formed on an overlapping surface between the first plate-shaped    member and the second plate-shaped member.

According to the configuration, it is possible to manufacture a formedarticle whose strength is reinforced by bending the joint structure inwhich the first plate-shaped member and the second plate-shaped memberare joined by welding.

-   (3) The joint structure according to (1) or (2), wherein the first    plate-shaped member and the second plate-shaped member are further    joined to each other in an overlapping surface between the first    plate-shaped member and the second plate-shaped member.

According to the configuration, it is possible to more firmly join thefirst plate-shaped member and the second plate-shaped member.

-   (4) The joint structure according to any one of (1) to (3), wherein    at least one of the first plate-shaped member and the second    plate-shaped member is a steel material for hot stamping.

According to the configuration, it is possible to form the jointstructure with an ultra-high strength steel plate.

-   (5) The joint structure according to any one of (1) to (4), which is    a structural member for an automobile.

According to the configuration, it is possible to manufacture the jointstructure that can be used as a structural member for an automobile.

-   (6) A method for manufacturing a joint structure formed by joining a    first plate-shaped member made of steel and a second plate-shaped    member made of steel that is overlapped on the first plate-shaped    member and that is formed in a long shape, the method including:

a step of overlapping the first plate-shaped member and the secondplate-shaped member; and

a welding step of joining each of both edge portions of the secondplate-shaped member along a longitudinal direction to the firstplate-shaped member by an arc welding or a laser-arc hybrid welding.

According to the configuration, it is possible to manufacture the jointstructure with high joining strength at low cost by bonding the firstplate-shaped member and the second plate-shaped member by an arc weldingor a laser-arc hybrid welding.

-   (7) The method for manufacturing a joint structure according to (6),    wherein a bending is performed on an overlapping surface between the    first plate-shaped member and the second plate-shaped member.

According to the configuration, it is possible to manufacture a formedarticle whose strength is reinforced, by bending the joint structure inwhich the first plate-shaped member and the second plate-shaped memberare joined by welding.

-   (8) The method for manufacturing a joint structure according to (6)    or (7), further comprising joining the first plate-shaped member and    the second plate-shaped member to each other in the overlapping    surface between the first plate-shaped member and the second    plate-shaped member by any welding of a laser welding, a plasma    welding, a TIG welding, or a laser-TIG hybrid welding.

According to the configuration, it is possible to more firmly join thefirst plate-shaped member and the second plate-shaped member.

-   (9) The method for manufacturing a joint structure according to any    one of (6) to (8), wherein at least one of the first plate-shaped    member and the second plate-shaped member is a steel material for    hot stamping.

According to the configuration, it is possible to form the jointstructure with an ultra-high strength steel plate.

-   (10) The method for manufacturing a joint structure according to any    one of (6) to (9), wherein the joint structure is a structural    member for an automobile.

According to the configuration, it is possible to manufacture the jointstructure that can be used as a structural member for an automobile.

Although the embodiments are described above with reference to thedrawings, it is needless to say that the present invention is notlimited to such examples. It will be apparent to those skilled in theart that various changes and modifications may be conceived within thescope of the claims. It is also understood that various changes andmodifications belong to the technical scope of the present invention.Constituent elements in the embodiments described above may be combinedfreely within a range not departing from the spirit of the presentinvention.

The present application is based on Japanese Patent Application No.2018-124515 filed on Jun. 29, 2018, the contents of which areincorporated herein by reference.

REFERENCE SIGNS LIST

-   10, 10A, 10B joint structure-   11 first plate-shaped member (steel material for hot stamping)-   11 a surface-   12 second plate-shaped member (steel material for hot stamping)-   12 a, 12 b edge portion-   13 weld metal (bead)-   14 overlapping surface-   15 joint portion-   16 bent portion-   17 joint portion-   20 formed article (structural member for automobile)-   30 B pillar

1. A joint structure formed by joining a first plate-shaped member madeof steel and a second plate-shaped member made of steel that isoverlapped on the first plate-shaped member and that is formed in a longshape, wherein a surface of the first plate-shaped member and both edgeportions of the second plate-shaped member along a longitudinaldirection are joined by a weld metal.
 2. The joint structure accordingto claim 1, wherein a bent portion is formed on an overlapping surfacebetween the first plate-shaped member and the second plate-shapedmember.
 3. The joint structure according to claim 1, wherein the firstplate-shaped member and the second plate-shaped member are furtherjoined to each other in an overlapping surface between the firstplate-shaped member and the second plate-shaped member.
 4. The jointstructure according to claim 1, wherein at least one of the firstplate-shaped member and the second plate-shaped member is a steelmaterial for hot stamping.
 5. The joint structure according to claim 1,which is a structural member for an automobile.
 6. A method formanufacturing a joint structure formed by joining a first plate-shapedmember made of steel and a second plate-shaped member made of steel thatis overlapped on the first plate-shaped member and that is formed in along shape, the method comprising: overlapping the first plate-shapedmember and the second plate-shaped member; and joining each of both edgeportions of the second plate-shaped member along a longitudinaldirection to the first plate-shaped member by an arc welding or alaser-arc hybrid welding.
 7. The method for manufacturing a jointstructure according to claim 6, wherein a bending is performed on anoverlapping surface between the first plate-shaped member and the secondplate-shaped member.
 8. The method for manufacturing a joint structureaccording to claim 6, further comprising joining the first plate-shapedmember and the second plate-shaped member to each other in theoverlapping surface between the first plate-shaped member and the secondplate-shaped member by any welding of a laser welding, a plasma welding,a TIG welding, or a laser-TIG hybrid welding.
 9. The method formanufacturing a joint structure according to claim 6, wherein at leastone of the first plate-shaped member and the second plate-shaped memberis a steel material for hot stamping.
 10. The method for manufacturing ajoint structure according to claim 6, wherein the joint structure is astructural member for an automobile.
 11. The joint structure accordingto claim 2, wherein the first plate-shaped member and the secondplate-shaped member are further joined to each other in an overlappingsurface between the first plate-shaped member and the secondplate-shaped member.
 12. The joint structure according to claim 2,wherein at least one of the first plate-shaped member and the secondplate-shaped member is a steel material for hot stamping.
 13. The jointstructure according to claim 2, which is a structural member for anautomobile.
 14. The method for manufacturing a joint structure accordingto claim 7, further comprising joining the first plate-shaped member andthe second plate-shaped member to each other in the overlapping surfacebetween the first plate-shaped member and the second plate-shaped memberby any welding of a laser welding, a plasma welding, a TIG welding, or alaser-TIG hybrid welding.
 15. The method for manufacturing a jointstructure according to claim 7, wherein at least one of the firstplate-shaped member and the second plate-shaped member is a steelmaterial for hot stamping.
 16. The method for manufacturing a jointstructure according to claim 7, wherein the joint structure is astructural member for an automobile.